It's probably already at maximum volume but you could try pressing the key combination that increases the volume. On most laptops you need to look for a key marked 'Fn', noting the colouring of its lettering (e.g. blue). Then you look for a key that's got a 'louder' symbol in the same colour (which is typically a picture of loudspeaker with sound coming out of it) and press both keys together.
It's also worth remembering that (for example) Youtube has its own volume control (underneath the video image). You need to ensure that such controls are also set to maximum.
It could be that the output to the speakers on your laptop just isn't very loud. Most laptops just don't have the capacity to produce very loud sound. Separate speakers ( see post above) would improve it no end though.